This disclosure relates generally to ionographic or electrophotographic imaging and printing apparatuses or reproduction machines, and more particularly is directed to a constrained transfer assist blade assembly for contacting a printing media.
Electrostatographic printing includes the well-known process of transfer. In transfer, charged toner particles from an image-bearing photoreceptor member are transferred to an image support substrate or print media, such as a copy sheet. Transfer is accomplished at a transfer station, wherein the transfer occurs by electro-statically overcoming adhesive forces holding the toner particles to the image-bearing member, thus transferring the developed toner image to the substrate.
In conventional electrostatographic machines, transfer is achieved by transporting the image support substrate into the area of the transfer station. The transfer station applies electrostatic force fields sufficient to overcome the adhesive forces holding the toner to the photoreceptor surface in order to attract and transfer the toner particles onto the image support substrate. In general, such electrostatic force fields are generated by means of electrostatic induction using a corona-generating device such as, for example, a dicorotron. The copy sheet is placed in direct contact with the developed toner image on the photoreceptor surface while the reverse side of the copy sheet is exposed to a corona discharge. This corona discharge generates ions having a polarity opposite to that of the toner particles, thereby electro-statically attracting and transferring the toner particles from the photoreceptive member to the image support substrate.
During electrostatic transfer of a toner image to a copy sheet, it is important for the copy sheet to be held in direct, uniform and intimate contact with the photoconductive surface and the toner image developed thereon. Unfortunately, however, the interface between the photoreceptive surface and the copy substrate is not always optimal. Various substrate conditions such as copy sheets being mishandled, wrinkled, creased, left exposed to the environment, or previously processed by a heat and pressure fusing or fixing operation, result in insufficient substrate contact with the photoreceptor surface during transfer. This substrate condition creates spaces or air gaps between the developed image on the photoreceptor surface and the copy sheet. The air gaps, in turn, impair transfer of the toner image, thus causing copy defects.
It is known to use a transfer assist blade (TAB) in the transfer process. Such transfer assist blades mechanically press the print media into substantially uniform intimate contact with the image-bearing surface, just prior to the build-up of the transfer electrostatic field. However, an electrostatic interaction may occur between the TAB member and the copy substrate. This is because the transfer-assist pressure blade is located in the transfer zone between the transfer corona-generating device, such as a dicorotron, and the photoreceptor. As a result, a measurable electrostatic charge is imparted on the blade member by the transfer dicorotron. In particular, the TAB tends to delaminate at higher actuation speeds that lead to print defects and backside sheet contamination. Once the TAB tip becomes charged, for example, the blades can splay from one another in a fan pattern. This type of delamination is undesirable since the blade tips are moved from their original positioning closer to the photoreceptor. This change in positioning means that the blades can either swipe through process control patches along the photoreceptor or can be close enough that they electro-statically attract the toner and contaminate the backside lead edge of the next print media or sheet.
As a result, to solve the problem of delamination at high speed printing, there is a need for an improved TAB that substantially eliminates the unwanted delamination of the TAB.